A β-glucan is a substance, of which components of saccharides are polymerically bonded. There is reported that the β-glucan exhibits many physiological actions such as an action to improve an immune strength, antitumor action, cholesterol-lowering action, antiviral action, and an action to improve the number of leukocytes. In recent years, the β-glucans attract attentions as health foods, medicaments, and so on.
The above-described β-glucan is included in a cell wall of a yeast. There have been proposed many varied processes for obtaining the polysaccharide such as the β-glucan. For instance, in JP-A-2003-197, there is disclosed a process for obtaining a composition including a polysaccharide which comprises a lot of intact β-glucan, which is biologically highly active, by bacteriolyzing a yeast by effecting a protease, in particular, an enzyme agent, of which total glucanase activity is especially little. In addition, JP-A-2002-209598 proposes a process for obtaining a soluble polysaccharide, which consists of the steps of: physically pulverizing a yeast by using a high pressure homogenizer; autolyzing the yeast; and causing an action of a cell-wall digesting enzyme on a fraction of a rinsed yeast cell wall. There is disclosed that a soluble polysaccharide including a lot of β-glucan can be produced in high yield.
Further, in JP-A-11-508772, there is disclosed a process for obtaining a β-glucan-mannan preparation by separating a solid content from a product, which is obtained by autolyzing a germ cell at a pH of 5˜6 and at a temperature of 35° C.˜60° C. for 6˜48 hours. In addition, in JP-A-11-500159, there is disclosed a process for preparing a chitosan-glucan complex. In this process, the chitosan-glucan complex is prepared by a partial deacetylation, which consists of the steps of: treating a bacteria, which comprises a chitin, with an alkali solution; treating thus obtained product with a dilute mineral acid; and further treating the product with an alkali solution having a high alkalinity.
In JP-A-9-512708, there is disclosed a process for preparing an insoluble β-(1-3)-glucan particle by treating a yeast cell which comprises a glucan, by respectively using a suitable water-soluble alkali solution for extraction, an acid for hydrolysis, and an ethanol, etc. Further, in JP-A-9-322795, there is disclosed that a solution containing a microorganism fungus body, which has, as a component thereof, a water-insoluble glucan such as a yeast is treated with an oxide having a predetermined concentration and with a hydroxide which adjusts a pH of the solution to 10˜12.5, simultaneously. JP-A-9-322795 explains that this process simultaneously realizes cell destruction, bleaching, and viscosity drop of a producing microorganism. Accordingly, the water-insoluble glucan can be effectively purified.
However, above-described processes for obtaining the glucan by using an alkali, an acid, and an organic solvent, there are needed treatments such as neutralization and demineralization, which make the processes of the production complicated. In addition, if the products are provided as foods, these processes leave an anxiety in relation to a safety of the products. Moreover, these processes are not preferable in terms of the yields, either. Further, in the process in which an enzyme agent is used, there is an anxiety that the glucan may be degraded with amylase, etc., included in the enzyme agent, which leads to a problem that it is difficult to obtain a highly effective long chain glucan. Further, there cannot be sufficiently removed lipid in the yeast cell of the glucan obtained by the above-mentioned processes, so that there is an anxiety that the obtained product may be colored by an oxidation of the lipid, or an oxidation off-flavor may be generated.